A buffer solution is typically an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or a weak base and its conjugate acid, and has the property that the pH of the solution changes very little when a small amount of strong acid or base is added to it. Buffer solutions are therefore used as a means of keeping pH at a nearly constant value in a wide variety of chemical applications, including e.g. chromatography, filtration, etc. In general, a buffer solution may be made up of more than one weak acid and its conjugate base. For instance, a wider buffer region may be created by mixing two buffering agents with overlapping individual buffer regions.
A buffer solution having a desired pH, and optionally, with a desired ionic strength, may be prepared by calculating the necessary amounts of the ingredients of the buffer and mixing them. While it is often necessary to solve several different equations for calculating the pH of a relatively simple mixture of a weak acid (or base) and a weak base (or acid) depending on their relative concentrations, there is commercial software available for performing such calculations.
Another possibility is to use feedback control as in WO/2011/162666 where the accuracy of the pH measurement limits the accuracy of the pH of the buffer. However calibration of pH meters is both time consuming and often troublesome. The pH meters may not be very accurate, have slow responses and may be easily contaminated by salts for example. The pH measurement is also dependent on temperature, with different buffers having a variety of temperature constants. Usually the reading of the pH meters cannot be corrected to a standard temperature.
Thus, there is still a need within the art to improve pH-measurements and to provide reliable instruments for this purpose.